In order to investigate the macroscopic and mesoscopic mechanism of hydration instability of rock-grout structure under the influence of moisture content, a direct shear test combined with particle flow code (PFC) sim...
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In order to investigate the macroscopic and mesoscopic mechanism of hydration instability of rock-grout structure under the influence of moisture content, a direct shear test combined with particle flow code (PFC) simulation was conducted subject to various moisture content levels and normal stresses. The results show that a higher moisture content would compromise the load bearing capacity of soft rock anchorage structures by deteriorating the structural integrity of the surrounding rock and the bonding effect between the anchorage interfaces. The load bearing capacity of the surrounding rock is also rapidly reduced. The rock-grout structure has four main shear damage modes, which are influenced by both moisture content and normal stress. When the saturated moisture content is reached, the anchorage structure has lost its bearing capacity, and the rock is muddied and subsequently debonded from the bolt. The energy required to break the internal adhesion of the rock-grout structure under the effect of hydration is greatly reduced, resulting in easy decoupling and dispersion between the rock skeleton particles. In turn, the rock surface particles bonded by the anchor agent are separated from the deeper particles, resulting in the failure of the bonding surface and weakening the coupling effect between the anchor and the surrounding rock. According to the test results, the control measures for surrounding rock of muddy roadway are put forward. The impact of water on the co-bearing capacity between rock and anchorage agent was analyzed, elucidating the shear mechanical characteristics and macro failure modes of the rock-grout structure during hydration. The meso-mechanical mechanism of hydration damage of rock-grout was obtained by analyzing microcrack distribution, stress evolution and energy consumption in rock-grout. Through microscopical and macroscopical tests, the process of hydration instability of rock-grout developing from microscopical damage to macroscopical
Grottoes encounter significant challenges, such as weathering and water erosion, seriously threatening their preservation. Current laboratory research on grotto deterioration predominantly centers on characterizing th...
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Grottoes encounter significant challenges, such as weathering and water erosion, seriously threatening their preservation. Current laboratory research on grotto deterioration predominantly centers on characterizing the deterioration process, making it challenging to conduct cross-scale quantitative analysis of the intricate rock evolution process. This study examines sandstone from Baoding Mountain in Dazu and employs a cross-scale experimental approach to conduct dry-wet cycle tests on salt weathering. By integrating particleflow numerical simulation and inorganic salt deliquescence theory, the study elucidates the mechanism of aging degradation of sandstone caused by various salt solutions. The results indicate that the hierarchical order of the influence of salt solution types on rock degradation, ranked from highest to lowest, is as follows: sodium sulfate, magnesium sulfate, and sodium carbonate. The sandstone samples exhibited significant damage after 7 and 18 cycles of medium and high-concentration sodium sulfate solutions, respectively. In contrast, the strength of sandstone samples decreased by only 5.3% on average after 20 cycles of medium and low-concentration sodium carbonate solution. Subsequently, particleflow was analyzed numerically using the variable stiffness theory. The influence of salt solution on sandstone's strength, deformation characteristics, internal pores, and fracture development can be quantitatively evaluated by examining five core mesoscopic parameters. Furthermore, the study highlights that the relative humidity required for the deliquescence of sodium sulfate and magnesium sulfate crystals exceeds 80%, making these crystals vulnerable to the repetitive dissolution-migration-precipitation processes in the climate conditions of Baoding Mountain, thereby accelerating the deterioration of rocks in the region. A cross-scale quantitative and qualitative research method considering aging degradation.A quantitative evaluation index system
Horizontal stratified cemented tailings backfill (SCTB) inevitably appears in the underground stope. Exploring the mechanical characteristics of horizontal SCTBs and explaining the strength deterioration mechanism of ...
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Horizontal stratified cemented tailings backfill (SCTB) inevitably appears in the underground stope. Exploring the mechanical characteristics of horizontal SCTBs and explaining the strength deterioration mechanism of horizontal SCTBs is essential for the strength design of backfill. In this study, experiments were used to investigate, on a macro-scale, the mechanical characteristics of horizontal SCTBs with varying filling interval time. Numerical simulations were utilized to explore the primary elements determining the strength of horizontal SCTBs from the micro-scale. The results show that, at the macro-scale, the interval time has an impact on the samples' mechanical properties by affecting the stratified surface's initial width. The change in the stratified surface's initial width leads to a change in the stratified surface's stiffness, which affects the mechanical properties of the sample. At the micro-scale, neither the stratified surface's bonding strength nor its friction coefficient significantly affects the mechanical properties of horizontal SCTBs. The monti-form bulges with different heights reduce the stratified surface's stiffness. Axial stress causes microcracks to form easily close to the stratified surface, destroying the sample's integrity and reducing SCTB's strength. The stiffness and number of stratified surfaces are the key variables impacting the mechanical properties of the horizontal SCTBs.
Understanding the failure process in surrounding rocks is essential for assessing the stability of underground spaces and predicting potential disasters. Although failure patterns around openings of various shapes hav...
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Understanding the failure process in surrounding rocks is essential for assessing the stability of underground spaces and predicting potential disasters. Although failure patterns around openings of various shapes have been studied, the effects of geological discontinuities on the characteristics of failure zones around these openings remain inadequately understood. This study investigates failures around openings and flaws by analyzing acoustic emission (AE) characteristics. Digital image correlation (DIC) was employed to measure the failure zones of specimens during experiments, and particle flow code (PFC) software modeled the failure process. A statistical tool quantitatively assessed the cumulative number-strain curves of AE events, distinguishing between different distribution modes (single- or multi-peak). Additionally, the magnitude distribution and source mechanisms of AE events were analyzed to evaluate the effects of exposure conditions and flaw inclination angles on AE event occurrence. Both experimental and numerical results showed strong agreement, demonstrating that exposure conditions and flaw inclination angles significantly affect AE event distribution and magnitude. Exposed flaws tended to suppress AE events on the side containing the flaws, whereas unexposed flaws promoted AE events on the side with flaws, with this effect varying based on flaw inclination angles. These findings provide valuable insights into the fracture characteristics of surrounding rocks in deep underground spaces affected by geological discontinuities.
The concentration of internal stress and the accumulation of energy within coal bodies are key factors that can trigger catastrophic events, such as rock bursts and gas outbursts. Therefore, understanding the internal...
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The concentration of internal stress and the accumulation of energy within coal bodies are key factors that can trigger catastrophic events, such as rock bursts and gas outbursts. Therefore, understanding the internal stress characteristics of coal is essential. The cuttings method, a commonly used detection technique, is often employed to reflect the degree of stress concentration in coal bodies. However, there is currently insufficient research on the relationship between the weight of cuttings and the stress of the coal body, making it difficult to quantitatively and accurately represent the actual stress state of the surrounding rock in boreholes. This study investigates the relationship between cuttings weight and coal body stress through both theoretical analysis and numerical simulation. Theoretically, a formula for calculating the weight of cuttings under a uniform stress field was derived, based on an analytical solution for the stress and displacement of surrounding rock in boreholes. The sensitivity of cuttings weight to changes in coal body stress is thoroughly analyzed. From a numerical simulation perspective, a discrete element method for coal drilling is developed, revealing the correlation between cuttings weight and coal body stress under both uniform and non-uniform stress conditions, as well as the impact of initial damage on cuttings weight. Additionally, a continuous damage model is constructed of the surrounding rock along the depth dimension, investigating how cuttings weight varies with drilling depth. Based on these findings, an automatic method is proposed for weighing cuttings to locate and estimate the magnitude of lateral stress peaks in roadway-surrounding rock. Field application experiments demonstrate the effectiveness of this method, yielding promising predictive results. The findings of this research provide both technical methods and theoretical support for using cuttings weight to quantitatively characterize coal body stress, whic
In the process of coal mining with complex hydrological conditions, underground coal seams are often subjected to corrosion by acidic water, and acidic water-rock chemical interactions can significantly affect the mec...
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In the process of coal mining with complex hydrological conditions, underground coal seams are often subjected to corrosion by acidic water, and acidic water-rock chemical interactions can significantly affect the mechanical properties of coal rocks, posing challenges for mine tunnel support and coal seam stability. This study investigates the effects of acidic solution exposure, specifically varying pH levels, on the mechanical and structural properties of coal samples. Static Brazilian splitting tests were conducted to determine the tensile mechanical properties of the treated coal samples. Additionally, the particle flow code (PFC) was utilized to examine the evolution of microcracks, stress fields, and energy conversion characteristics within the coal samples. The results indicate that acidic solutions induce damage and softening of the coal structure, leading to a reduction in tensile strength and elastic modulus as acid corrosion intensifies. The primary mechanism of failure in the coal samples is attributed to the initiation, propagation, nucleation, and rapid consolidation of microcracks within stress concentration zones. A decrease in the area of stress concentration zones, increased stress unevenness, and reduced ultimate tensile strength in corroded coal samples lead to more complex crack propagation paths and lower macroscopic strength. Energy monitoring further reveals that acid-corroded coal has reduced resistance to damage and higher failure rates, highlighting the heightened vulnerability of acid-affected coal in structural applications.
The stress state of composite rock joints has a significant impact on the overall stability of the rock mass. Studying the composite mechanism disk specimens with different matrix strengths and inclination angles unde...
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The stress state of composite rock joints has a significant impact on the overall stability of the rock mass. Studying the composite mechanism disk specimens with different matrix strengths and inclination angles under Brazilian splitting state is of great significance for improving the safety of surrounding rock. This research conducted Brazilian tests on different types of jointed composite disk specimens at different inclination angles and explored the effects of inclination angle and material strength on the mechanical properties and deformation characteristics of specimens. Clarified the failure mechanism of joint specimen. The experimental results indicate that the disk specimens under different inclination angles exhibit three typical failure modes. As the inclination angle increases, failure mode changes from Disk matrix failure (DM failure) to Disk matrix and structural failure (DMS failure), and ultimately to Disk structural failure (DS failure). Failure load, input energy, and strain energy of the specimen continue to decrease as the inclination angle increases and the matrix strength decreases. The decrease in matrix material significantly weakens the strength of the specimen, but this effect continues to decrease with the increase of inclination angle. DIC results show that as the inclination angle increases, the position of cracks exists from the loading end to the joint surface. Through theoretical analysis, it is found that as the inclination angle increases, the stress state at the center of the specimens changes from compression-shear state to shear state, and finally to tension state, corresponding to three failure modes: DM failure, DMS failure, and DS failure, respectively.
Repeated rainfall usually results in the weakening of the strength characteristics of the engineered rock masses, which can induce engineering accidents. To explore the effect of water-induced rock strength damage und...
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Repeated rainfall usually results in the weakening of the strength characteristics of the engineered rock masses, which can induce engineering accidents. To explore the effect of water-induced rock strength damage under the repeated action of saturation and drying, this study conducted compression experiments on red sandstone. Laboratory experiments were combined with numerical simulations aimed at analyzing strength damage patterns and crack evolution characteristics. The results show that drying-wetting cycles have a strong deterioration effect on the physico-mechanical properties, particularly during the initial cycle, which causes the greatest damage. As the number of cycles increases, the number of tensile cracks decreases, the number of tensile-shear cracks increases, and the number of compression-shear cracks is stable. The particle contact force chain becomes thicker and denser, and the particle displacement direction gradually changes from "center to both sides" to "center to top and bottom." The crack evolution process under uniaxial compression was divided into four stages: crack-free, crack emergence, crack propagation, and crack sharp increase stage. When the cracks progressed to the crack propagation stage, macroscopic fracture of the rock was imminent. This may be an indicative precursor of rock damage.
The Fenwei Basin, covered by loess, experiences severe ground fissure disasters. These disasters disrupt the continuity of the loess and pose significant threats to engineering construction safety along transportation...
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The Fenwei Basin, covered by loess, experiences severe ground fissure disasters. These disasters disrupt the continuity of the loess and pose significant threats to engineering construction safety along transportation routes. Nevertheless, the crack characteristics and the influence zone of ground fissures in the loess layer remain inadequately investigated. To effectively prevent and control ground fissure disasters, physical model tests and the PFC(particle flow code) numerical simulation method are used to investigate the crack mechanism of buried ground fissures in the loess layer. The results show that there are two main cracks in the layer profile, which have a Y-shape morphology. As the dip angle of the preset cracks increased from 60° to 90°, the main deformation zone at the surface gradually shifted towards the footwall. The process of crack propagation from depth to surface is divided into five stages. Additionally, the results confirm the accuracy of the width of the rupture zone d2in the footwall calculated by the cantilever beam theory. These findings can offer theoretical guidance for determining the avoidance distance of ground fissures in loess regions, as well as for implementing disaster prevention and corresponding control measures for various stages of buried ground fissure propagation.
The creep behavior of rocks significantly impacts projects' structural safety, including mining, tunneling, and hydraulic engineering. Numerous creep models used in numerical calculations incorporate basic element...
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The creep behavior of rocks significantly impacts projects' structural safety, including mining, tunneling, and hydraulic engineering. Numerous creep models used in numerical calculations incorporate basic elements, such as Burger's model. However, relying solely on series or parallel combinations of these basic components fails to account for the accelerated creep stage, prompting efforts toward developing enhanced creep models. Despite noted progress, a limited number of studies on the full-process simulation of graded creep loading and the consequent generation of cracks. To overcome this problem, an innovative creep model is proposed based on both the Parallel Bond and the Kelvin-Voigt contact models. This proposed creep model simulates the graded loading creep test of rocks under different load conditions and also conducts a parameter sensitivity analysis for the impact of the proportionate discrepancy between the two contact models. The results indicate that this new creep model could successfully simulate the comprehensive creep process, effectively capture crack progression, and represent ultimate failure modes during the creep process. Notably, to ensure the precision of simulations, it is recommended that the proportion of the Kelvin-Voigt contact model within the total contact is at most 25%.
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